Ios 如何创建具有真实持续时间的虚拟AVPlayerItem？

我正在使用

AVPlayer

在

AVSynchronizedLayer

上播放

CAKeyFrameAnimations

。为了在动画期间不播放

AVAsset

时保持播放器播放，我将

AVPlayerItem

的

forwardPlaybackEndTime

设置为所需动画的持续时间。不幸的是。在这个

forwardPlaybackEndTime

期间，似乎不可能

seekToTime:

，因为

AVPlayer

总是回到开头。可能是因为它试图寻找

AVplayerItem

的持续时间

---

我怎样才能创建一个具有真实持续时间的虚拟AVPlayerItem来欺骗AVPlayer播放一些空的

AVPlayerItem

，并让我

seekToTime

？

不幸的是，

seekToTime

只会搜索

AVPlayerItem的持续时间。因此，需要创建一个虚拟玩家项目来生成可搜索的持续时间。为了快速执行此操作，需要创建一个虚拟AVplayerItem。下面是生成此类项的实现示例。它很长，但它是必需的。祝你好运

@interface FakeAsset ()

+ (CVPixelBufferRef)blackImagePixelBuffer;

@end

@implementation FakeAsset

+ (void)assetWithDuration:(CMTime)duration
        completitionBlock:(void (^)(AVAsset *))callBack
{
    NSError * error      = nil;
    NSString * assetPath = nil;
    NSUInteger i         = 0;
    do
    {
        assetPath =
        [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"dummyAsset%i.m4v",i]];
        i++;
    }
    while ([[NSFileManager defaultManager] fileExistsAtPath:assetPath
                                                isDirectory:NO]);

    NSURL * fileURL = [NSURL fileURLWithPath:assetPath];

    NSParameterAssert(fileURL);

    AVAssetWriter * videoWriter =
    [[AVAssetWriter alloc] initWithURL:fileURL
                              fileType:AVFileTypeAppleM4V
                                 error:&error];
    NSParameterAssert(videoWriter);

    NSDictionary * compression  =
  @{
    AVVideoAverageBitRateKey      : @10,
    AVVideoProfileLevelKey        : AVVideoProfileLevelH264Main31,
    AVVideoMaxKeyFrameIntervalKey : @300
    };

    NSDictionary * outputSettings =
  @{
    AVVideoCodecKey                 : AVVideoCodecH264,
    AVVideoCompressionPropertiesKey : compression,
    AVVideoWidthKey                 : @120,
    AVVideoHeightKey                : @80
    };

    AVAssetWriterInput * videoWriterInput =
    [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                       outputSettings:outputSettings];
    NSParameterAssert(videoWriterInput);

    NSDictionary * parameters =
    @{(NSString *)kCVPixelBufferPixelFormatTypeKey : @(kCVPixelFormatType_32ARGB),
      (NSString *)kCVPixelBufferWidthKey           : @120,
      (NSString *)kCVPixelBufferHeightKey          : @80
      };

    AVAssetWriterInputPixelBufferAdaptor * adaptor =
    [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:videoWriterInput
                                                                     sourcePixelBufferAttributes:parameters];
    NSParameterAssert(adaptor);
    NSParameterAssert([videoWriter canAddInput:videoWriterInput]);

    videoWriterInput.expectsMediaDataInRealTime = NO;

    [videoWriter addInput:videoWriterInput];

    NSParameterAssert([videoWriter startWriting]);

    [videoWriter startSessionAtSourceTime:kCMTimeZero];

    dispatch_queue_t dispatchQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    [videoWriterInput requestMediaDataWhenReadyOnQueue:dispatchQueue
                                            usingBlock:^
    {
        int frame = 0;
        while (videoWriterInput.isReadyForMoreMediaData)
        {
            if (frame < 2)
            {
                CMTime frameTime = frame ? duration : kCMTimeZero;
                CVPixelBufferRef buffer = [self blackImagePixelBuffer];

                [adaptor appendPixelBuffer:buffer
                      withPresentationTime:frameTime];

                CVBufferRelease(buffer);

                ++frame;
            }
            else
            {
                [videoWriterInput markAsFinished];
                [videoWriter endSessionAtSourceTime:duration];

                dispatch_async(dispatch_get_main_queue(), ^
                {
                    [videoWriter finishWritingWithCompletionHandler:^()
                     {
                         NSLog(@"did finish writing the video!");
                         AVURLAsset * asset =
                         [AVURLAsset assetWithURL:videoWriter.outputURL];
                         callBack(asset);
                     }];
                });
                break;
            }
        }
    }];
}

+ (CVPixelBufferRef)blackImagePixelBuffer
{
    NSDictionary * options =
    @{
      (id)kCVPixelBufferCGImageCompatibilityKey         : @YES,
      (id)kCVPixelBufferCGBitmapContextCompatibilityKey : @YES
      };

    CVPixelBufferRef pxbuffer = NULL;
    CVReturn status =
    CVPixelBufferCreate(kCFAllocatorDefault, 120, 80, kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef)options, &pxbuffer);

    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);

    void * pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    //kCGImageAlphaPremultipliedFirst
    CGContextRef context = CGBitmapContextCreate(pxdata, 120, 80, 8, 4*120, rgbColorSpace, (CGBitmapInfo)kCGImageAlphaNoneSkipFirst);

    NSParameterAssert(context);
    CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor);
    CGContextFillRect(context,CGRectMake(0.f, 0.f, 120.f, 80.f));
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

@接口伪造资产（）
+（CVPixelBufferRef）blackImagePixelBuffer；
@结束
@实施伪造资产
+（作废）资产持续时间：（CMTime）持续时间
completionblock：（void（^）（AVAsset*）回调
{
n错误*错误=nil；
NSString*assetPath=nil；
整数i=0；
做
{
资产路径=
[NSTemporaryDirectory（）stringByAppendingPathComponent:[NSString stringWithFormat:@“dummyAsset%i.m4v”，i]]；
i++；
}
而（[[NSFileManager defaultManager]文件存在路径：assetPath
董事会：否）；
NSURL*fileURL=[NSURL fileURLWithPath:assetPath]；
NSParameterAssert（fileURL）；
视频写手=
[[AVAssetWriter alloc]initWithURL:fileURL
文件类型：AVFileTypeAppleM4V
错误：&错误]；
NSParameterAssert（视频编写器）；
NSDictionary*压缩=
@{
AVVideoAverageBitRateKey:@10，
AVVideoProfileLevelKey:AVVideoProfileLevelH264Main31，
AVVideoMaxKeyFrameIntervalKey:@300
};
NSDictionary*输出设置=
@{
AVVideoCodeKey:AVVideoCodecH264，
AVVideoCompressionProperties键：压缩，
AVVideoWidthKey:@120，
AVVideoHeightKey:@80
};
AVAssetWriterInput*视频写入器Input=
[AvassetWriteInput AssetWriteInputWithMediaType:AVMediaTypeVideo
outputSettings:outputSettings]；
NSParameterAssert（videoWriterInput）；
NSDictionary*参数=
@{（NSString*）kCVPixelBufferPixelFormatTypeKey:@（kCVPixelFormatType_32ARGB），
（NSString*）kCVPixelBufferWidthKey:@120，
（NSString*）kCVPixelBufferHeightKey:@80
};
AvassetWriterInputPixelBufferAdapter*适配器=
[AvassetWriterInputPixelBufferAdapter AssetWriterInputPixelBufferAdapter WithAssetWriterInput:videoWriterInput
sourcePixelBufferAttributes：参数]；
NSParameterAssert（适配器）；
NSParameterAssert（[videoWriter canAddInput:videoWriterInput]）；
videoWriterInput.expectsMediaDataInRealTime=否；
[videoWriter附加输入：videoWriterInput]；
NSParameterAssert（[videoWriter startWriting]）；
[videoWriter startSessionAtSourceTime:kCMTimeZero]；
调度队列调度队列=调度获取全局队列（调度队列优先级默认为0）；
[VideoWriterInputRequestMediaDataWhenRepayonQueue:dispatchQueue
使用块：^
{
int帧=0；
while（videoWriterInput.isReadyForMoreMediaData）
{
如果（帧<2）
{
CMTime frameTime=帧？持续时间：KCMTIME0；
CVPixelBufferRef缓冲区=[self blackImagePixelBuffer]；
[像素缓冲区：缓冲区]
withPresentationTime:frameTime]；
CVBufferRelease（缓冲区）；
++框架；
}
其他的
{
[videoWriterInput markAsFinished]；
[videoWriter EndSessionSourceTime:持续时间]；
dispatch\u async（dispatch\u get\u main\u queue（）^
{
[videoWriter使用CompletionHandler完成写入：^（）
{
NSLog（@“视频写完了！”）；
AVURLAsset*资产=
[avurlaste assetwithur:videoWriter.outputURL]；
收回（资产）；
}];
});
打破
}
}
}];
}
+（CVPixelBufferRef）blackImagePixelBuffer
{
NSDictionary*选项=
@{
（id）kCVPixelBufferCGImageCompatibilityKey:@是，
（id）kCVPixelBufferCGBitmapContextCompatibilityKey:@YES
};
CVPixelBufferRef pxbuffer=NULL；
返回状态=
CVPixelBufferCreate（kCFAllocatorDefault、120、80、KCVpixelFormattType_32ARGB、（__桥CFDictionaryRef）选项和pxbuffer）；
NSParameterAssert（状态==kCVReturnSuccess&&pxbuffer！=NULL）；
CVPixelBufferLockBaseAddress（pxbuffer，0）；
void*pxdata=CVPixelBufferGetBaseAddress（pxbuffer）；
NSParameterAssert（pxdata！=NULL）；
CGColorSpaceRef rgbColorSpace=CGColorSpaceCreateDeviceRGB（）；
//KCGIMAGEAlphaPremultipledFirst
CGContextRef context=CGBitmapContextCreate（pxdata，120,80,8,4*120，rgbColorSpace，（CGBitmapInfo）kCGImageAlphaNoneSkipFirst）；
NSParameterAssert（上下文）；
CGContextSetFillColorWithColor（上下文[UIColor blackColor].CGColor）；
CGContextFillRect（上下文，CGRectMake（0.f，0.f，120.f，80.f））；
CGBColorSpace；
CGC